Segmented duct seal

ABSTRACT

Confronting faces of a segmented duct of circular cross-section are provided with mutually opposing grooves running transverse to the front plane of the duct, the grooves each having a tapered surface, the tapered surfaces of opposing grooves being in mutually facing relationship with each other. A thin flat rectangular plate bridges the gap between the tapered surfaces, having one of its longitudinal edges resting on each surface. A net force on the plate created for example by a pressure differential across the plate results in a seal between the tapered surfaces and each plate edge, thereby preventing the radial leakage of fluid through the gap between the segments.

United States Patent [191 Bowers et al.

[ 11 Aug. 14, 1973 SEGMENTED DUCT SEAL [73] Assignee: United AircraftCorporation, East Hartford, Conn.

[22] Filed: Nov. 17, 1971 [21] Appl. No.: 199,552

[52] US. Cl. 415/173, 415/217 2,934,316 4/1960 Watson et a] 415/1363,146,992 9/1964 Farrell 415/136 3,542,483 1 l/ 1970 Gagliardi 3,551,06812/1970 Scalzo et a1 415/173 Primary Examiner-C. J. HusarAttorney-Charles A. Warren ABSTRACT Confronting faces of a segmentedduct of circular cross-section are provided with mutually opposinggrooves running transverse to the front plane of the duct, the grooveseach having a tapered surface, the tapered surfaces of opposing groovesbeing in mutually facing relationship with each other. A thin ilatrectangular plate bridges the gap between the tapered surfaces, havingone of its longitudinal edges resting on each surface. A net force onthe plate createdfor example by a pressure differential across the plateresults in a seal between the tapered surfaces and each plate edge,thereby preventing the radial leakage of fluid through the gap betweenthe segments.

5 Claims, 6 Drawing Figures Patented Aug. 14, 1973 FIGJ N f M 2% DFSEGMENTED DUCT SEAL The invention herein described was made in thecourse of or under a contract with the Department of the Air Force.

BACKGROUND OF THE INVENTION 1. Field of Invention This inventionrelates, generally, to a seal for preventing radial leakage of fluidbetween the segments of a segmented duct.

2. Description of the Prior Art A duct having a curvilinearcrosssection, inner and outer surfaces and front and back edges is oftenused to separate two fluids. This duct, for example, may constitute aportion of the gas path wall in a gas turbine engine, with cooling airflowing along one surface and the working fluid flowing along the other.In some instances the duct will be subjected to high temperatures whichwill cause it to expand creating undesirable stresses within the duct.For this and other reasons the duct may be cut from its front to backedge in several locations forming longitudinal segments havingconfronting faces therebetween. Gaps are provided between theconfronting faces to allow for thermal expansion. If the fuilds on eachside of the duct are under different pressures, leakage will occurthrough the gaps. In order to prevent this radial leakage of fluidthrough these gaps a sealing means must be provided.

It is known to provide opposing grooves of rectangular cross-section insaid confronting faces, running from the front to the back of thesegments. Within the cavity formed by the opposing grooves is a flatthin rectangular plate which is of sufficient width to bridge the gapbetween the segments. A pressure differential across the plate forcesthe plate toward the inner or outer surface of the duct against thesurfaces of the grooves. As long as these groove surfaces remainsubstantially parallel and in the same plane, good sealing isaccomplished over the length of the plate. However, due to thermalexpansion and also because of unavoidable hardware'tolerances of theparts these surfaces often move with respect to one another becomingmisaligned and skewed. The plate isthen unable to maintain sufficientcontact with the surfaces and is thus unable to provide a good seal. itis apparent, for example, that even if the surfaces are parallel a smallamount of mismatch between the grooves in a direction perpendicular tosaid surfaces may result in the plate resting on the surface of only onegroove without coming into any contact with the surface of the opposinggroove. Additionally, if said surfaces are skewed with respect to oneanother, maintaining contact along the entire length of both surfaceswould require that the plate bend around the edge of one of the grooves.One or the other lengthwise edges of the plate will then necessarilylift off the surface of one of the grooves leaving a clear path throughwhich fluid can leak. The plate is, of course, limited in flexibilityand would not be able to provide good sealing under such circumstancesunless said skewness were extremely small.

Another method which has been used in the past to seal such a gap is atongue and groove along the confronting faces running from the front tothe back of the segments. But sealing problems exist with the tongue andgroove design to an even greater extent because the tongue, beingintegral with one of the segments, is even less flexible than a separateplate.

SUMMARY OF INVENTION Accordingly it is an object of the presentinvention to provide a sealing means to prevent radial leakage of fluidthrough the gaps of a segmented duct.

It is a further object of the present invention to provide sealing meansbetween said gaps wherein the sealing means does not interfere with thethermal expansion of the segments and provides adequate sealingthroughout said thermal expansion.

It is another object of the present invention to provide sealing meansbetween said gaps wherein the sealing capability is maintained despiteradial mismatch and skewness between the segments.

According to the present invention, a duct of curvilinear cross-section,adapted to separate two fluids under different pressures, is made up oflongitudinal segments said segments having confronting faces transverseto the plane of the front edge of the duct, said faces being insubstantially parallel relationship to each other with gaps therebetweenwherein at least one longitudinal groove is provided within each face,said groove being in opposing relationship to the groove in theconfronting face, each groove having at least one tapered surface, saidsurface being in mutually facing relationship with the taper surface onthe opposing groove; a plate is disposed within said opposing grooves,wide enough to bridge the gap therebetween, the longitudinal edges ofsaid plate adpated to contact said mutually facing tapered surfaces,said plate being responsive to a force which presses the plate intocontinuous sealing contact with said tapered surfaces thus preventingradial leakage through the gap between the segments.

This force may be created by a pressure differential, centrifugal load,spring, or'other means. If the force is sufficiently large the platewillbend until it conforms itself to the tapered surface. In that case aneven better seal will be created by the surface-to-surface contactinstead of the line-on-line seal which simple edge contact wouldprovide. Except for the limits of the flexibility of the plate itself,there is nothing to prevent the edges or surface of the plate fromcoming into contact with the tapered surfaces even though these surfacesmay be misaligned or skewed with respect to one another. As hereinbeforediscussed, the prior art seal with rectangular grooves is severelylimited in its sealing capability under such conditions.

It can be seen that this invention does not in any way interfere withthe relative motion between the segments as would the aforementionedtongue and groove seal. Also, as already stated, since the tongue isintegral with one of the segments it has limited flexibility. Generallythe tongue and groove design relies on close tolerances to perform itssealing function. Comparative testing between a tongue and groove designandthis invention, as it is hereinafter described in the preferredembodiment, has shown that the sealing effectiveness of this inventionis four times that of a tongue and groove.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent in the light of the followingdetailed description of the preferred embodiment thereof as illustratedin the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partly sectioned, partialelevation view of a first stage turbine vane assembly embodying theinvention',

FIG. 2 is a developed partial sectional view partly broken away takenalong the line 2-2 in FIG. 1, with the inner turbine casing removed;

FIG. 3 is a sectional view taken along the line 3-3 in FIG. 2, rotated90, particularly illustrating the invention;

FIG. 4 is a sectional view taken along line 33 in FIG. 2, rotated 90,showing an alternate form of the invention;

FIG. 5 is a sectional view taken along line 3-3 in FIG. 2 rotated 90;and

FIG. 6 is a partly sectioned, partial elevation view of a rotor assemblyembodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2,a first stage turbine stator assembly 10 of a gas turbine engine isspaced downstream of a burner duct 12 and includes an outer turbinecasing 14, including a flanged ring 16, and an inner turbine casing 15providing support for a plurality of stator vanes 17 circumferentiallydisposed between said casings, each vane comprising a substantiallyradial airfoil 18 having a central void 19, an inner shroud 20 having anairfoil shaped hole 21 communicating with the central void 19, and anouter shroud 22 having a similar hole (not shown) also communicatingwith said central void 19, said shrouds forming the inner and outerwalls 24 and 26, respectively, of an annular gas path 28 which receiveshot gas from the burner 12. Each airfoil 18 is also provided with holes30 connecting the central void 19 of the airfoil with the gas path 28.Each inner and outer shroud 20 and 22 is provided with an upstreamflange 32 and 34, respectively, for attachment to turbine casings l4 and15 by pins 35. An inner annular chamber 36 and an outer annular chamber38 formed between the supporting structure 14 and 15 and the vaneshrouds 20 and 22, are provided with cooling air under pressure which isfed into the holes 21 in each of the inner and outer shrouds, throughthe hollow airfoils 18, and out holes 30 to cool the surfaces of theairfoils. In order to obtain maximum efflciency and to maintain propercooling of the vanes 17, the air in the gas path 28 must be keptseparated from the cooling air in chambers 36 and 38. Gaps 40 betweenadjacent shrouds 20 in FIG. 2, and similar gaps (not shown) between theshrouds 22, provided to allow for thermal expansion, must be sealed toprevent radial leakage therethrough.

Although hereinafter the description is restricted to the seal betweenthe inner shrouds 20 it should be V noted that a similar sealing meansis used between the outer shrouds 22. Each pair of adjacent shrouds 20has confronting faces 42 (FIGS. 2 and 3). Said faces are each providedwith grooves 44 (FIGS. 1-3). The grooves run substantially from theupstream end of the face to the downstream end of the face. As bestshown in FIGS. 2 and 3, the grooves on confronting faces are insubstantially opposing relationship to one'another, and each has aninner and outer surface 46, 47, respectively, and a bottom surface 53.Both the inner surface 46 and the outer surface 47 of each groove aretapered,

the taper angles 48 and 49 between face 42 and the surface 46 and 47,respectively, being greater than A thin flat rectangular plate 50 isdisposed within said facing grooves. A net force on the plate created bythe difference in gas pressure in the chamber 36 and in the gas path 28causes the plate to be pressed against the pair of mutually facingtapered surfaces 46 (or 47 depending on the direction of the force)forming a seal be tween the edges 51 of the longitudinal sides 52 of theplate and the tapered surfaces 46 preventing radial leakage of fluid. Asshown in FIG. 4, in accordance with the invention, the tapered surfacesof the grooves may be the bottom surfaces 53a of the grooves 44a.

As the plate becomes thinner and as the pressure differential across theplate increases the seal between the edges of the plate and the taperedsurfaces becomes better. Best possible sealing is achieved when theplate is made thin enough such that the pressure differential across theplate forces it to bend until it conforms with the tapered surfaces ofthe grooves as shown in FIG. 5. Under these conditionssurface-to-surface contact is obtained at 54 and 55. It is desirable,however, that the plate regain its original shape when the force isremoved because the grooves do not remain exactly in the samerelationship to one another during engine operation. The plate must alsobe able to withstand the forces on it. Thus, if the taper is too steepor the plate too thin, the plate may bend past its tensile limits andbreak or not return to its original shape. If the plate is not flexibleenough and the taper is too steep the flexibility limits of the platemay prevent proper sealing even along the edges 51. In any event, aftera certain point, as the plate is further decreased in thickness there isa diminishing return in increased sealing effectiveness because most ofthe sealing has already been accomplished. If the taper is too shallowthe groove approaches a rectangular cross-section and the seal will havethe problems associated with a rectangular shape as hereinbeforediscussed.

Another consideration in the design of this seal and one which may oftendetermine the final groove configuration is the fact that the plateshould not be able to fall out of the grooves. In the preferredembodiment if this should happen the plate might end up in the enginegas path 28 and damage other parts further downstream. Thus, in FIG. 3the width of the plate 50in conjunctiori with the depth and opening ofthe grooves 44, should be such as to prevent the plate from being ableto rotate and fall into the gap 40 between the shrouds. Also, the bottom53 of the groove should be wide enough so that the plate cannot becomewedged between the surfaces 46 and 47.

In a typical operation of an engine incorporating an embodiment of theinvention the temperature of the cooling air in the chamber 36 is about1,100F and the temperature in the gas path 28 near the wall 24 is about2,250F resulting in a temperature differential across the plate 50 ofapproximately 1,150F. Typical pressures in the chamber 36 and the gaspath 28 are 380 psi and 280 psi, respectively, resulting in a pressuredifferential across the plate of approximately psi. Under theseconditions AMS 5536 is a suitable material for the plate. The plate is0.009 inch thick with a width of 0.215 inch. The taper angles 48 and 49are both 1430, and the groove opening is 0.120 inch while the groovedepth is 0.1 15 inch. As stated hereinbefore, the seal of thisembodiment has reduced leakage by afactor of four over a tongue andgroove design operating under identical conditions.

There is the possibility in this application that the force across theplate would reverse directions due to changing pressures in the gas path28 and in the chambers 36 and 38. For this reason both sides 46 and 47of the grooves are tapered so that sealing will be accomplished if thepressure in the chamber 36 is either higher than or lower than thepressure in the gas path 28. FIGS. 3 through 5 show the position of theplate when the former condition exists. If that condition were the onlyone possible, then the surface 47 would not need to be tapered.

Also, in this embodiment the grooves 44 do not extend across the fulllength of the shroud faces 42 and thus the plate 50 is trapped by theends 62 of the grooves. An alternate configuration mighthave the groovesextending across the full length of the shroud faces; in such a case,end plates or other suitable means at the upstream and downstream endsof the grooves may be utilized to trap the plate.

FIG. 6 shows a further application for this invention. A portion of arotor assembly 70 of a gasturbine engine is shown. Said rotor assemblycomprises a hub 71 and a plurality of rotor blade assemblies 72. Each ofsaid rotor blade assemblies comprises an airfoil 73, an inner shroud 74and a fir tree shaped root 76. Said fir tree shaped root is attached tosaid hub by means of fir tree shaped slots 77 in said hub. Confrontingfaces 80 of adjacent shrouds 74 each contain a groove 82. These groovesare similar in design to the grooves hereinabove described for thestator vane assembly. In this application, however, the groove surfacewhich is tapered is the radially outermost surface 84. A flat plate 88is disposed within a pair of opposing grooves. The centrifugal forcecreated by the rotating hub 71 will press said plate into sealingrelationship with the tapered surfaces 84.

Although the invention has been shown and described with respect to apreferred embodiment thereof, it should be understood by those skilledin the art that the foregoing and various other changes and omissions inthe form and detail thereof may be made therein without department fromthe spirit and the scope of the invention.

Having thus described a typical embodiment of our invention, that whichwe claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A fluid pressure seal assembly, which comprises:

a duct adapted to separate fluids which are under different pressures,said duct having a circular cross section and comprising a plurality oflongitudinal segments, adjacent segments having confronting faces eachface having at least one length-wise groove to provide at least one pairof opposing lengthwise grooves in said confronting faces, each groove ofsaid pair having at least one tapered surface, the tapered surface ofone groove being in mutually facing relationship with the taperedsurface of the opposing groove; and

a plurality of flat plates each loosely disposed within a related pairofopposing grooves, and each having two straight parallel longitudinaledges, said longitudinal edges of said plate, in the presence of aradial fluid pressure differential, being in fluid sealing contact withsaid mutually facing tapered surfaces of opposing grooves to provide afluid seal between said confronting faces solely as a result of thefluid pressure acting on said plate :in a radial direction.

2. The fluid pressure seal assembly according to claim 1 wherein saidplate is flexible and additional contact between the surface of theplate and the mutually facing tapered surfaces occurs in the presence ofa fluid pressure differential.

3. A turbine stator assembly comprising:

an annular inner casing;

an annular outer casing surrounding said inner casing thereby forming anannular passageway therebetween;

a plurality of vanes, said vanes distributed circumfer entially withinsaid annular passageway and each comprising an inner shroud, an outershroud, and an airfoil therebetween, said shrouds forming the inner andouter walls of an annular gas path in the gas turbine engine, each ofsaid airfoils having a central void, and each of said shrouds having asubstantially radial hole therethrough which communicates with saidairfoil central void forming a passageway through each of said vaneswith an opening at both ends, each airfoil also having a plurality ofholes forming passageways between said gas path and said central void,adjacent shrouds of each gas path wall having confronting faces, with atleast one pair of opposing grooves in said confronting faces, eachgroove of said pair having at least one tapered surface, the taperedsurface of one groove being in mutually facing relationship with thetapered surface of the opposing groove;

said inner and outer casings further comprising structure for supportingsaid inner and outer shrouds and for forming an inner annular chamberbetween said inner shrouds and said inner casing, and an outer annularchamber between said outer shrouds and said outer casing, said outerannular chamber and said inner annular chamber adapted to carry gasesunder pressures higher than gas path pressures for feeding through theholes in said inner and outer shrouds, into the central voids of theairfoils, out the holes in the airfoil connecting the central void withthe gas path, and finally cooling the outer surface of the airfoils,;and

a plurality of flat plates, each having two straight parallellongitudinal edges, each disposed within a related pair of said opposinggrooves in the inner and outer shrouds, said edges being adapted tocontact the mutually facing tapered surfaces of the grooves in thepresence of a pressure differential acrosssaid plate to provide a fluidseal between said confronting faces.

4. The assembly according to claim 3 wherein said plate is flexible and,in the presence of a pressure differential across said plate, is forcedinto additional fluid sealing contact between the surface of the plateand the mutually facing tapered surfaces.

5. A turbine stator assembly comprising:

an annular inner casing;

an annular outer casing surrounding said inner casing thereby forming anannular passageway therebe-- a related pair of opposing grooves in saidshrouds, and each having two straight parallel longitudinal edges, saidedges of said plate, in the presence of a radial fluid pressuredifferential, sealingly contacting said mutually facing tapered surfacesof opposing grooves to provide a fluid seal between said confrontingfaces solely as a result of the fluid pressure acting on said plate in aradial direction.

1. A fluid pressure seal assembly, which comprises: a duct adapted toseparate fluids which are under different pressures, said duct having acircular cross section and comprising a plurality of longitudinalsegments, adjacent segments having confronting faces, each face havingat least one length-wise groove to provide at least one pair of opposinglengthwise grooves in said confronting faces, each groove of said pairhaving at least one tapered surface, the tapered surface of one groovebeing in mutually facing relationship with the tapered surface of theopposing groove; and a plurality of flat plates each loosely disposedwithin a related pair of opposing grooves, and each having two straightparallel longitudinal edges, said longitudinal edges of said plate, inthe presence of a radial fluid pressure differential, being in fluidsealing contact with said mutually facing tapered surfaces of opposinggrooves to provide a fluid seal between said confronting faces solely asa result of the fluid pressure acting on said plate in a radialdirection.
 2. The fluid pressure seal assembly according to claim 1wherein said plate is flexible and additional contact between thesurface of the plate and the mutually facing tapered surfaces occurs inthe presence of a fluid pressure differential.
 3. A turbine statorassembly comprising: an annular inner casing; an annular outer casingsurrounding said inner casing thereby forming an annular passagewaytherebetween; a plurality of vanes, said vanes distributedcircumferentially within said annular passageway and each comprising aninner shroud, an outer shroud, and an airfoil therebetween, said shroudsforming the inner and outer walls of an annular gas path in the gasturbine engine, each of said airfoils having a central void, and each ofsaid shrouds having a substantially radial hole therethrough whichcommunicates with said airfoil central void forming a passageway througheach of said vanes with an opening at both ends, each airfoil alsohaving a plurality of holes forming passageways between said gas pathand said central void, adjacent shrouds of each gas path wall havingconfronting faces, with at least one pair of opposing grooves in saidconfronting faces, each groove of said pair having at least one taperedsurface, the tapered surface of one groove being in mutually facingrelationship with the tapered surface of the opposing groove; said innerand outer casings further comprising structure for supporting said innerand outer shrouds and for Forming an inner annular chamber between saidinner shrouds and said inner casing, and an outer annular chamberbetween said outer shrouds and said outer casing, said outer annularchamber and said inner annular chamber adapted to carry gases underpressures higher than gas path pressures for feeding through the holesin said inner and outer shrouds, into the central voids of the airfoils,out the holes in the airfoil connecting the central void with the gaspath, and finally cooling the outer surface of the airfoils,; and aplurality of flat plates, each having two straight parallel longitudinaledges, each disposed within a related pair of said opposing grooves inthe inner and outer shrouds, said edges being adapted to contact themutually facing tapered surfaces of the grooves in the presence of apressure differential across said plate to provide a fluid seal betweensaid confronting faces.
 4. The assembly according to claim 3 whereinsaid plate is flexible and, in the presence of a pressure differentialacross said plate, is forced into additional fluid sealing contactbetween the surface of the plate and the mutually facing taperedsurfaces.
 5. A turbine stator assembly comprising: an annular innercasing; an annular outer casing surrounding said inner casing therebyforming an annular passageway therebetween; a plurality of airfoils eachhaving an inner and outer end, said airfoils distributedcircumferentially within said annular passageway and each comprising ashroud at one end thereof, said shrouds forming a wall of an annular gaspath in a gas turbine engine, said inner and outer casings furthercomprising structure for supporting said inner and outer ends of saidairfoils, adjacent shrouds of said gas path wall having confrontingfaces, with at least one pair of opposing grooves in said confrontingfaces, each groove of said pair having at least one tapered surface, thetapered surface of one groove being in mutually facing relationship withthe tapered surface of the opposing groove; and a plurality of flatplates each loosely disposed within a related pair of opposing groovesin said shrouds, and each having two straight parallel longitudinaledges, said edges of said plate, in the presence of a radial fluidpressure differential, sealingly contacting said mutually facing taperedsurfaces of opposing grooves to provide a fluid seal between saidconfronting faces solely as a result of the fluid pressure acting onsaid plate in a radial direction.